This is a very important topic. All logical aspects would seem to suggest that stored cellular blood components have an immune suppressive effect.

However, it is questionable whether this study can really document this effect. The difference in the number of transfused older blood units in the first 12 hours between the patients developing infectious complications and those without, is the same as for transfused blood units altogether.

Therefore, the reviewer’s conclusion is that patients having received significantly more blood units in the first 12 hours also received significantly more often older blood and therefore developed significantly more infections.

One might speculate that these patients have been more severely ill, and therefore received more blood. These patients were (not significantly) older, had (not significantly) higher injury severity
score, had clearly more often blunt trauma (propylactic antibiotics in penetrating injury?), and had (not significantly) higher serum lactate levels.

– V. Kretschmer